Why is it important to claim your baby on your taxes?

My mother in law is trying to claim my baby next year. I don’t want her to (she doesn’t provide anything for my daughter, no clothes, diapers, food, child care, nothing) but we do live with her. My boyfriend makes more than I do so I want him to claim her. I suck at doing taxes though so I don’t know much about the subject. When I tell her no and that we want to claim her, what can my reasoning be? Like I honestly just don’t understand why it’s important for the parents to claim the child.